The Hanoverian Army of Observation was a field army of the Electorate of Hanover during the Seven Years' War. The army was formed by King George II of Great Britain with 27,000 men from Hanover, 10,000 from Hesse-Kassel, 1,600 from Saxe-Gotha-Altenburg, 6,000 from Brunswick-Wolfenbuttel, and 1,350 men from Schaumburg-Lippe. Led by Prince William, Duke of Cumberland, the Army of Observation was defeated at the Battle of Hastenbeck in July 1757, and Cumberland's ensuing declaration of neutrality in September resulted in the French occupation of Hanover, Hesse, Brunswick, and Schaumburg-Lippe. King George, who did not approve the ceasefire, sacked his son and resumed the war effort after the November Battle of Rossbach. Duke Ferdinand of Brunswick-Wolfenbuttel was given command of the re-recruited Anglo-Hanoverian army, and he liberated Hanover and expelled the French in the spring of 1758, preventing a new occupation of Hanover and driving the French back even further over the following years.